It is known that a conventional wave plate induces a given phase difference (retardation) to polarization components of light emitted from an optical source such as a laser light source and thereby, adjusts the polarization direction of the light emitted from the optical source to output light for which the polarization direction is controlled. Wave plates include, for example, λ/2 wave plates that induce a phase difference of λ/2 (where, λ is the wavelength of the light) on polarization components and λ/4 wave plates that induce a phase difference of λ/4 on polarization components. A wave plate, for example, that uses polarization film to transmit light of an amount that corresponds to the polarization direction is employed in an attenuator. Further, to implement a broadband wave plate, a stacked wave plate is known that is a combination of plural wave plates (for example, refer to Patent Documents 1 and 2 below).
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2008-070690
Patent Document 2: Published Japanese-Translation of PCT Application, Publication No. 2003/091768